1. Field of the Invention
This invention relates generally to an exposure control system for a photographic apparatus and more particularly to an exposure control system having a follow focus capability for a photographic apparatus of the type having means for initiating the energization of a source of artificial light to illuminate a photographic screen.
2. Description of the Prior Art
The exposure system of a photographic camera when operated in conjunction with a flash or transient illumination is ordinarily adjusted as a function of the levels of illumination anticipated at the scene being photographed. An evaluation based on the anticipated level of illumination may be made based upon an application of the inverse square law of light energy propagation which may additionally be weighted to anticipate spurious room reflections. under this law, the light energy available from a given source is considered to vary inversely with the square of the distance from that source. Accordingly, to make an appropriate exposure mechanism adjustment for flash photography, source to subject distance is derived and the value of this distance is utilized to compute an appropriate exposure value or illuminational factor.
In some camera designs, exposure control adjustment for flash operation is effected automatically by incorporating within the apparatus what is termed as a follow focus system. With a follow focus arrangement, aperture adjustment or flash illumination output control is mechanically coupled with the range finding or focusing system of a camera. In effect, a follow focus control represents a second exposure control system for a camera. As such, its presence necessarily contributes to the size and complexity of the camera.
A follow focus control system for an exposure control system is described in a U.S Patent entitled "Focus Responsive Exposure Control System" by V. K. Eloranta and E. K. Shenk, Ser. No. 3,750,543, filed Apr. 19, 1971, and assigned in common herewith. The patent describes a second flash mode control system wherein an electromagnetic device, such as a solenoid, is selectively maneuvered and energized to extend its plunger to arrest position of exposure aperture blades in accordance with focal setting. A complete follow focus system is described in a U.S. Patent entitled "Apparatus and System for Flash Photography" by Lawerence M. Douglas, filed Mar. 15, 1973, Ser. No. 3,832,722 and assigned in common herewith. This system achieves a requisite compactness to meet the overall camera design described in U.S. Pat. No. 3,714,879 and incorporates means for selective use of the follow focus system exclusively during the flash illuminated exposure mode of operation. The above follow focus system additionally provides a trim function to accomodate for slight variations in the sensitometric characteristic of the film as well as to insert a modicum of personal or overriding control over the automated system. The trim control has only one control element for operation in this manner substantially reducing the possibility that a camera operator may become confused or overlook a requirement for providing a trim control for that mode of operation for which he is currently using.
It is therefore a primary object of this invention to provide an improved exposure control system with follow focus capability for a photographic apparatus of the type having means for initiating the energization of a source of artificial light to illuminate a photographic scene.
It is also an object of this invention to provide an improved exposure control system with follow focus capability for a photographic apparatus wherein a selected aperture may be uniformly trimmed by a predetermined number of F/stops regardless of the actual focus setting of the photographic apparatus.
It is a further object of this invention to provide an improved exposure control system with follow focus capability wherein the mechanism may be precisely calibrated despite the cumulative effect attributable to the dimensional variations of the individual components albeit such variations remain within prescribed tolerances.
It is an additional object of this invention to provide an improved exposure control system having follow focus capability wherein the geometrical orientations of the mechanical components are determined in a select manner to provide uniform adjustment of the exposure aperture through a trim mechanism irrespective of the actual focus setting.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.